1. Field of the Invention
This invention relates to a lead frame for semiconductor devices, and more particularly, to a lead frame having a plurality of leads for connecting electrodes of a semiconductor chip accommodated in a package to external terminals. This invention also relates to a process for making such a lead frame for semiconductor devices.
2. Description of the Related Art
A conventionally known semiconductor device has a semiconductor chip accommodated in a package made of resin, ceramic or the like. Usually, a lead frame therefor is formed by integrally stamping or punching a thin metal strip, or etching the same and providing a plurality of leads which are used for connecting electrodes of a semiconductor chip accommodated in the package to external terminals.
Such a lead frame is usually formed as a longitudinal strip of continuous segments of lead frame units connected in series in the longitudinal direction. Each lead frame unit includes a square-shaped stage for mounting a semiconductor chip thereon and a plurality of leads radially arranged side by side with a small clearance therebetween at peripheral regions of the respective sides of the stage.
The semiconductor chip is provided with a plurality of electrodes on the periphery of a chip surface, but the number or arrangement of such electrodes differs for each individual semiconductor chip, according to the purpose, function, use or the like thereof.
Therefore, conventionally various kinds of lead frames must be prepared in order to adapt them to the various kinds of semiconductor chips, i.e., a particular lead frame has a predetermined number and arrangement of leads adapted to a semiconductor chip in question. Thus precision dies must be used to form the various kinds of lead frames, thereby increasing manufacturing costs.
To form a lead frame in which a plurality of leads are arranged at the peripheral regions of a square-shaped stage, with the tips of the respective leads coated with an aluminum thin film, the following steps are conventionally required. Namely, a lead frame is first formed by integrally stamping or punching a thin metal strip, or etching the same. The leads distributed in the four peripheral regions are then subjected to, for example, vacuum vapor deposition, to deposit aluminum onto the tips of the leads of each lead frame unit. Accordingly, large-scale machinery, such as a vacuum vapor deposition apparatus or the like, and much labor are required.